Crystal detector



0er. 29,v 1946. w, L. CARLSON l, 2,410,268

CRYSTAL DETECTOR Filed Feb. A26, 1942 Sli/60N CYSTHL 0575670@ 5 Enventor Y I @gwn y Gttorneg Patented Oct. 29, Y1946 CRYSTAL DETECTOR..

Wendell L. Carlson, Haddonlield, N. J.,assignor to Radio Corporation of America, a corporaftion of Delaware ApplicationFebruary 26, 1942,.v Serial'No. 432,381

This invention relates to improvements in crystal detectors for use inthe demodulation, rectification and detection of oscillations of radio frequency.

There are two general types of detectors: the crystal rectifier and the vacuum tube rectifier. The vacuum tube rectifier has almost entirely supplanted the crystal rectier in the "detection of oscillations within the frequency bands now commonly employed in the transmission of intelligence. However, it is now appreciated by those skilled in the radioart that there are certain signalling systems which lend themselves more readily to the use of a crystal rectifier than to a vacuum type rectifier.

The principal object of the present invention is to provide an improved crystal detector, and one highly sensitive to oscillations of ultra-high frequencies. Another and specific object of the present invention is to provide a silicon detector of enhanced sensitivity, and to provide a simple, inexpensive and reliable method of sensitizing such crystals.

In the accompanying drawing:

Fig. 1 is a View in perspective of a crystal detector element showing one form of instrument which may be employedvin sensitizing said element in accordance with the method of the invention, Fig. 2 is a. view in perspective of the sensitized crystal detector and showing one form of contact therefor, and Fig. 3 shows, in crosssection, another form o-f contact for the crystal.

The foregoing and related objects are achieved in accordance with the invention by the application of an extremely thin deposit, layer, or film of a ferrous metal, oxide or alloy thereof, to the exposed or contact surface ofthe silicon or equivalent crystal. This deposit, or layer, or lm may be submicroscopic in character, that is to say, the added metal particles comprising the deposit may be so fine and so sparsely distributed as to prevent visual observation when examined under a SOO-power light microscope, yet must be in a quantity or of a character suflicient to pro- .12 claims. (erase-.31)

duce a positive reaction when the treated sur-y face is subjected to certain standard chemical tests for the presence of ferrous materials.

The ferrous material may be deposited on the surface of the crystal by thermal evaporation in vacuo, by cathodic disintegration, by electrolysis,

precipitation, or by any other conventional method. However, in using such methods, diculties may be experienced in achieving a. deposit of the requisite distribution and particle size.l It

has been `found that the desired sensitization can be simply'achieved by rubbing or stroking the surface to be treated with a piece of iron or steel.

In carrying the invention into effect, the silicon or other crystal S which is to be sensitized may be ground to a flat surface or to a V-shape or knife-like edge, V. The crystal is then preferably, but not necessarily, etched in a concenftrated solution of sodium hydroxide and the residue removed. Such solution may comprise 50 grams NaOH in 50 cc. of H2O at 90 C. Thereafter, and in accordance with the invention, a deposit of a ferrous metal, oxide or alloy thereof is applied to the said V-edge, or other contact surface, either by one of the above mentioned conventional deposition methods or, more simply, by rubbing or stroking the said surface with an iron wire or steel needle N (Fig. 1). A very few strokes will usually suice to greatly increase the number of highly sensitive contact points on the crystal.

The sensitized crystal may then ibe mounted in a conventional manner with its sensitized surface or edge V presented to a cat whisker or other suitable contact C. The contact C may comprise a conventional round wire, as shown in Fig. 2, or it may be cuneifo'rm, in cross section, as shown at C' in Fig. 3. The sharpened contact portion may be made by grinding or filing the wire of Fig. 2.

At present it is only possible to theorize as to the reason for the improved operating characteristics of silicon crystals which have been treated in accordance with the invention. It is believed that rectification of radio frequency oscillations cannot be achieved with chemically pure silicon and that the impurities, principally iron, present in commercial grades of silicon are essential to rectication. Accordingly, it may be that the ferrous impurities necessary to rectification are not evenly distributed in commercial grades of silicon and that the added ferrous deposit of the present invention supplies the missing ingredient in the necessary quantity and with the necessary distribution on the surface of the crystal.

What is claimed is:

l. Method of increasing the sensitivity of a silicon element to oscillations of radio frequency, said method comprising forming a ferrous deposit y on a surface of said silicon.

2. Method of increasing the sensitivity of a said method comprising forming a sub-microscopic ferrous deposit on a surface of said sili- A stituted of discrete ferrous particles on a surface of sai-d silicon.' f .Y

4. Method of increasing the sensitivity of a piece of silicon to oscillations of radio frequency, said method comprising rubbing said silicon piece with a piece of ferrous material.

5. Method of increasing the sensitivity of a piece of silicon to oscillations of radio frequency said method comprising rubbing said silicon piece with a piece of iron.

6. Method of increasing the sensitivity of a piece of silicon to oscillations of radio frequency said method comprising rubbing said silicon piece with a piece of steel.

7. Method of increasing the sensitivity of a piece of silicon to oscillations of radio frequency,

4 said method comprising etching a surface of said silicon piece and thereafter forming a ferrous deposit on said etched surface.

8. Method of increasing the sensitivity of a piece of silicon to oscillations of radio frequency, said method comprising subjecting a surface of Said silicon piece to the action of sodium hydroxide and thereafter forming a ferrous deposit on said surface.

9. A crystal detector comprising a piece of silicon having a ferrous deposit on a surface thereof.

10. A crystal detector in accordance with claim 9 and wherein said deposit is sub-microscopic in character.

11. A crystal detector in accordance with claim 9 vand wherein said deposit is constituted essentially of discrete ferrous particles.

v12. The invention as set forth in claim 9 and wherein the surface to which said deposit is applied comprises a. knife edge. f

WENDELL L. CARLSON. 

